Herding Enemies

One of the finer points of Double Agent lies in "herding" your foes; this refers to the art of luring guards away from their default positions to where you can more stealthily take them down, and also to splitting up groups of foes so that you can dispatch them one by one without having them spot you and sound an alarm. Herding requires you to utilize both aural and visual clues to get your foes interested in you, but not interested enough to sound that damn alarm.

Sound Clues

There are a bunch of ways to utilize sound clues in Double Agent. If you make a sound that's loud enough to be distinguishable from any nearby ambient noises, enemies will usually come to investigate the source of the sound. If you intentionally make a sound while in a shadowy or poorly-lit area, then you can silently move a bit, wait for your foe to investigate the spot where you made the noise, then kill them or disable them without having to worry about moving their body around.

The built-in sound feature is whistling. If you're hiding out somewhere, and you want enemies to come to your position, then you can hit the whistle button to send out a whisper or whistle sound. This is easy to do, since it's a simple button press, but isn't very flexible. The untrained soldiers early in the game will come to investigate these like the dupes they are, but as you get around to facing the more well-trained mercs and government soldiers, the whistle won't be so useful, as the experienced soldiers will recognize it for a trap and refuse to get too close to the source of the whisper.

Perhaps a better source of sound is your footsteps. If you accelerate for a second while standing in the shadows, you should be able to make footsteps that rise above any ambient sound, which will almost always attract guards to the source.

The ultrasonic transmitter will help you shepherd people away from your position.

A situational form of noise maintenance comes in the form of objects that can be picked up and thrown across a room. There are plenty of varieties of these, such as plastic water bottles, soda cans, liquor bottles, etc. You need to be careful when using these objects, though, as if you accidentally hit your foe instead of throwing it near him, they'll sometimes start shooting at you right off. If you’re throwing a glass bottle, though, hitting them in the head will usually knock your foe out.

Lastly, the unlockable ultrasonic emitter is a great way to get soldiers interested in areas away from you. With it, you’ll be able to make sound originate from anywhere you can see, just by pulling a trigger. It won’t prevent soldiers from firing on you or checking out a more suspicious target, such as when they spot you moving through a lit area, but it can be great at getting soldiers away from their posts.

Visual Clues

Although getting seen is generally a Bad Thing for Sam, there is something of a twilight zone of lightedness in the first half of your light meter. If you're a good distance away from the enemy, and manage to walk into a light source so that you're only partially lit, but lit well enough to be seen, then your foe will usually decide that something's up and start walking over, but won't call in for backup or trip an alarm. This is arguably one of the best ways to lure foes in, but you'll need to make sure that you don't get too well lit, or they'll signal for help, and you'll also need to make sure that there's only one enemy that can spot you, or you may have to deal with two guards at the same time.